1. Field of the Invention
The present invention relates to a liquid crystal display device having different liquid crystal aligning domains in each of a plurality of minute unit regions.
2. Description of the Related Art
A liquid crystal display device comprises a liquid crystal panel having a pair of opposite transparent glass plates and a liquid crystal inserted between the glass plates. One of the glass plates has a common electrode and an alignment layer in the inner surface thereof and the other glass plate has a plurality of minute picture electrodes and an alignment layer in the inner surface thereof. Recently, an active matrix circuit with the picture electrodes is often formed in the latter glass plate. The alignment layers are treated by rubbing. In addition, polarizers are arranged on the outside of the glass plates, respectively. Usually, the polarizers are arranged so that the transmitting axes of the polarized light thereof are perpendicular to each other (normally white mode). The present invention is described below with reference to this normally white mode but it is needless to say that the present invention is applicable to a normally black mode (the transmitting axes of the polarized light are parallel to each other) regarding technically identical matters.
In the liquid crystal panel, molecules of the liquid crystal are aligned with a pretilt in accordance with the rubbing directions of the alignment layers in the glass plates. In the twisted nematic liquid crystal display device in which polarizers are arranged perpendicular to each other, the rubbing directions of the alignment layers in the glass plates are perpendicular to each other, and molecules of the liquid crystal twist helically from one of the glass plates to the other. Thus, when voltage is not applied to the liquid crystal, molecules of the liquid crystal are maintained in a condition maintaining the initial twist and the initial pretilt, and the incident light rotatingly propagates the liquid crystal along the twist and emits therefrom. In this case, a white spot is obtained in a normally white mode in which the polarizers are arranged perpendicular to each other. When voltage is applied, molecules of the liquid crystal rise, and the action of the birefringence of the liquid crystal becomes weak and the above rotating performance of the polarized light becomes weak, so that it becomes difficult for the incident light to transmit the liquid crystal display and a black spot is obtained. In this way, it is possible to form an entire image on the display having a contrast of brightness and darkness, by controlling the voltage applied to the liquid crystal.
When the voltage is applied to the liquid crystal, molecules of the, liquid crystal rise depending on the pretilt but all of the molecules of the liquid crystal between the opposite glass plates do not rise identically; some part of the molecules of the liquid crystal near the glass plates are restricted by the alignment layers and rises slightly, and some of the molecules of the liquid crystal located intermediately between the glass plates rise. Accordingly, it is mainly the performance of the molecules of the liquid crystal located intermediately between the glass plates that forms the black spot when voltage is applied.
Molecules of the liquid crystal have an elongated rod-like shape, and an action of birefringence differs when the polarized light impinges upon the liquid crystal from the direction of its long axis or from the direction of its short axis. Molecules of the liquid crystal do not rise perpendicular to the glass plates but rise at a certain angle relative to the glass plates. Accordingly, when molecules of the liquid crystal rise at a certain angle and an observer views the display from various angles, the direction of the long axis of the molecules of the liquid crystal relative to the observer varies and a variation of the transmittance of light occurs, resulting in a change in the obtained grayscale. For this reason, the contrast of brightness and darkness in the image is reduced depending on the position of the observer. This is generally recognized as a characteristic of a viewing angle of the liquid crystal.
To solve this problem, Japanese Unexamined Patent Publication (Kokai) No. 54-5754 discloses a liquid crystal display device having two different liquid crystal aligning domains in each of a plurality of minute unit regions. In this case, the direction of twist is different in the respective domains. Also, Japanese Unexamined Patent Publication (Kokai) No. 63-106624 discloses a liquid crystal display device having two different liquid crystal aligning domains in each of a plurality of minute unit regions. In this case, the direction of alignment is different in the respective domains. This domain divided liquid crystal display device may solve the characteristic viewing angle problem of the liquid crystal, by averaging two different viewing angle characteristics.
However, to obtain a liquid crystal display device having two different liquid crystal aligning domains in a minute unit region, it is necessary to effect an alignment treatment, i.e., a rubbing, to each of the alignment layers in one direction and then in another direction, using a mask or the like having minute openings, and such an alignment treatment should be made twice for each alignment layer. Also, it is known to form the mask having minute openings on the alignment layer by a photolithographic technique. A photo-resist is applied to the alignment layer, and minute openings are formed in the resist by a photolithographic technique. The alignment layer with the resist is then rubbed by a rubbing roller and the resist is removed from the alignment layer. This operation is then repeated with a resist having different minute openings and another rubbing.
Accordingly, there is an increase in the number of manufacturing steps for obtaining the domain divided liquid crystal display device which presents a problem. Also, there is a problem in that the rubbed alignment layers are damaged by the subsequent photolithographic operations, and the quality of the alignment layers deteriorate.